The revenue from the assessments imposed pursuant to this article by the district are trust funds and shall be encumbered only for the purposes for which the district is formed and for the benefit of the acreage assessed. The district shall expend the minimum amount necessary for overhead and other administrative costs. No district funds shall be donated, loaned, or transferred to any other local agency or to the state for any purpose, except for the implementation of the duties of the district, set forth under this article, as determined to be necessary by the district board.